Maximizing Efficiency

Discussion in 'General Slingshot Discussions' started by tiago_henrique, Oct 30, 2012.

  1. tiago_henrique

    tiago_henrique New Member

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    Hi Guys, <br><br>I´m from Brazil, and I became just amazed about this forum and blog. First of all I would like to congrat all of you for this initiative. <br><br>After see thousands of videos and tutorials, i really liked the Bullpup crossbow. I´ll try to make myself one, but before want to discuss some topics. <br><br>I want to fire 12mm lead balls with maximum efficiency. Do you guys know if we can get energy around 80 J shooting this size of ammo?<br><br>Here you can see some pictures of the Slingshot that me and my father have made for my little cousin. I have used local material (still waiting the thera band gold to arrive). <br><br>Do you guys have experience shooting at 50m? Can we hit a beer can at that distance?<br><br><a href="http://www.servimg.com/image_preview.php?i=3&u=17890782" class="postlink" target="_blank" rel="nofollow"><img src="http://i49.servimg.com/u/f49/17/89/07/82/th/foto411.jpg" border="0" alt=""></a><br><br><a href="http://www.servimg.com/image_preview.php?i=4&u=17890782" class="postlink" target="_blank" rel="nofollow"><img src="http://i49.servimg.com/u/f49/17/89/07/82/th/foto510.jpg" border="0" alt=""></a><br><br>I have some 16 and 22mm steel balls. Tomorrow I´ll chrony test the one that we made for my cousin just to have an idea of how much energy we can get out of it. I don't expect too much because we have used a poor quality rubber. Anyway, he is just 8 years old, so he is not crazy about power <img src="http://illiweb.com/fa/i/smiles/icon_wink.gif" alt="Wink" longdesc="15">
     
  2. MaddyMax

    MaddyMax New Member

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    hello and welcome!<br><br><table width="90%" cellspacing="1" cellpadding="0" border="0" align="center">
    <tr><td><span class="genmed"><b>tiago_henrique wrote:</b></span></td></tr>
    <tr><td class="quote">I want to fire 12mm lead balls with maximum efficiency. Do you guys know if we can get energy around 80 J shooting this size of ammo?</td></tr>
    </table>
    <span class="postbody"><br><br>with the right amount theraband gold it's possible. but not quite sure if there's enough draw lenght on this slingshot. 50 meters at a beercan is also possible with luck, training and under good weather conditions (and knowing about ballistic curves).</span>
     

  3. onnod

    onnod Im from Holland, isnt that weird?

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    welcome, yes we can, at 100 m we can and at 150 it is still possible, there are some cool youtube vids
     
  4. JoergS

    JoergS Administrator

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    A 12 mm lead ball weighs about 10 gramms. You would have to shoot it at 126 m/s = 413 fps. <br><br>Using rubber, that is highly unlikely, impossible with a handheld slingshot. I personally have never even seen a slingshot crossbow that could do that. Maybe a very very long (like 3 meters long) slingshot could do it, but even that is a big challenge. <br><br>Your bands would not last very long anyway, as an extreme tapering would have to be employed. <br><br>If you want 80 Joules, use heavier ammo. A .75" lead ball (19mm) weighs about 40 gramms, and you only have to shoot it at 63 m/s for 80 Joules. Much more realistic. And you get twice as much momentum from the 19mm lead ball, too.
     
  5. tiago_henrique

    tiago_henrique New Member

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    This morning I´ve done some chrony tests with my cousins slingshot:<br><br>with 16mm Steel balls - 126 fps (11 J)<br>with 22.5mm steel balls - 80 fps (13 J)<br><br>Ok, it´s not a lot, but he´s only 8 years old, i don´t want to modify the slingshot for more power. <br><br>I also have a barnnet Cobra slingshot, and it shoots the 16mm steel ball at 151 fps (17 J). <br><br>As soon as my thera-band arrive, I´ll start build my crossbow slingshot, and see how much energy I can get from 12mm lead balls. <br><br>I realized that 80 J with this size of ammo is virtually impossible, but i believe that something between 40-50 J is plausible.<br><br>Thank´s all for the answers.
     
  6. JoergS

    JoergS Administrator

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    With 12 mm lead balls, 35 Joules is already a very good result. 16 mm lead and 22 mm steel, yes, 50 Joules is well possible.
     
  7. Tobias

    Tobias New Member

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    i have made a vid with 13mm steel, i shoot it with more than 37 Joule, i can shoot the 16mm steel with 50 Joule.<br><br>your 12mm lead weight around as much as my 13mm steel.<br><br>i recommend you 1:2 tapered TB Gold with around 18kg draw weight and 160cm draw it´s around 40 Joule.
     
  8. tiago_henrique

    tiago_henrique New Member

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    with this set:<br><br>i recommend you 1:2 tapered TB Gold with around 18kg draw weight and 160cm draw it´s around 40 Joule.<br><br>How long is going to be the band life?
     
  9. FIAAO

    FIAAO Failureisalwaysanoption

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    <table width="90%" cellspacing="1" cellpadding="0" border="0" align="center">
    <tr><td><span class="genmed"><b>tiago_henrique wrote:</b></span></td></tr>
    <tr><td class="quote">This morning I´ve done some chrony tests with my cousins slingshot:<br><br>with 16mm Steel balls - 126 fps (11 J)<br>with 22.5mm steel balls - 80 fps (13 J)<br><br>Ok, it´s not a lot, but he´s only 8 years old, i don´t want to modify the slingshot for more power. <br><br>I also have a barnnet Cobra slingshot, and it shoots the 16mm steel ball at 151 fps (17 J). <br><br>As soon as my thera-band arrive, I´ll start build my crossbow slingshot, and see how much energy I can get from 12mm lead balls. <br><br>I realized that 80 J with this size of ammo is virtually impossible, but i believe that something between 40-50 J is plausible.<br><br>Thank´s all for the answers.</td></tr>
    </table>
    <span class="postbody"><br><br>Its not much, but its enough to be illegeal (without a licence) in Sweden <img src="http://illiweb.com/fa/i/smiles/icon_eek.gif" alt="Shocked" longdesc="5"></span>
     
  10. CEZ

    CEZ New Member

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    <table width="90%" cellspacing="1" cellpadding="0" border="0" align="center">
    <tr><td><span class="genmed"><b>Failureisalwaysanoption wrote:</b></span></td></tr>
    <tr><td class="quote">
    <table width="90%" cellspacing="1" cellpadding="0" border="0" align="center">
    <tr><td><span class="genmed"><b>tiago_henrique wrote:</b></span></td></tr>
    <tr><td class="quote">This morning I´ve done some chrony tests with my cousins slingshot:<br><br>with 16mm Steel balls - 126 fps (11 J)<br>with 22.5mm steel balls - 80 fps (13 J)<br><br>Ok, it´s not a lot, but he´s only 8 years old, i don´t want to modify the slingshot for more power. <br><br>I also have a barnnet Cobra slingshot, and it shoots the 16mm steel ball at 151 fps (17 J). <br><br>As soon as my thera-band arrive, I´ll start build my crossbow slingshot, and see how much energy I can get from 12mm lead balls. <br><br>I realized that 80 J with this size of ammo is virtually impossible, but i believe that something between 40-50 J is plausible.<br><br>Thank´s all for the answers.</td></tr>
    </table>
    <span class="postbody"><br><br>Its not much, but its enough to be illegeal (without a licence) in Sweden <img src="http://illiweb.com/fa/i/smiles/icon_eek.gif" alt="Shocked" longdesc="5"></span>
    </td></tr>
    </table>
    <span class="postbody"><br>OMG.. I was mad at Poland for not having crossbows legal here...</span>
     
  11. What would be about the maximum power you could get from a handheld shooter? I'm not as large as Joerg by any means so I probably won't be able to shoot anything near strong enough, I am just curious.
     
  12. JoergS

    JoergS Administrator

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    Shoot the heaviest ammo you can fire at 50 m/s. At that speed, you are shooting rather than throwing. <br><br>Heavy ammo is the key to high energy and momentum for rubber powered weapons. <br><br>For me, that would be the 25 mm steel ball. I can shoot it at about 55 m/s on a good day, almost 100 Joules, 3,5 N momentum. Crushes anything.
     
  13. Very nice, about what's the draw weight for momentums like that? I don't have a cronny so I have to go off of draw weight.
     
  14. onnod

    onnod Im from Holland, isnt that weird?

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    <table width="90%" cellspacing="1" cellpadding="0" border="0" align="center">
    <tr><td><span class="genmed"><b>JoergS wrote:</b></span></td></tr>
    <tr><td class="quote">A 12 mm lead ball weighs about 10 gramms. You would have to shoot it at 126 m/s = 413 fps. <br><br>Using rubber, that is highly unlikely, impossible with a handheld slingshot. I personally have never even seen a slingshot crossbow that could do that. Maybe a very very long (like 3 meters long) slingshot could do it, but even that is a big challenge.</td></tr>
    </table>
    <span class="postbody"><br>it is possible <a href="http://www.youtube.com/watch?v=eRzTCKMg-lY&feature=plcp" target="_blank" rel="nofollow">http://www.youtube.com/watch?v=eRzTCKMg-lY&feature=plcp</a></span>
     
  15. tiago_henrique

    tiago_henrique New Member

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    Very interesting video Onnod. <br><br>But the 10mm steel weights 4g, and the 1/2" lead ball (12,7mm) weights 12g. It´s 3 times more. <br><br>Do you think that the thera band blue will acelarete the 1/2" lead ball as fast as the 10 mm steel (of course we´ll need do add more layers)?<br><br>What about the thera-band black?
     
  16. onnod

    onnod Im from Holland, isnt that weird?

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    add more layers would do the trick i think
     
  17. Arturo Borquez

    Arturo Borquez Administrator

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    <table width="90%" cellspacing="1" cellpadding="0" border="0" align="center">
    <tr><td><span class="genmed"><b>onnod wrote:</b></span></td></tr>
    <tr><td class="quote">
    <table width="90%" cellspacing="1" cellpadding="0" border="0" align="center">
    <tr><td><span class="genmed"><b>JoergS wrote:</b></span></td></tr>
    <tr><td class="quote">A 12 mm lead ball weighs about 10 gramms. You would have to shoot it at 126 m/s = 413 fps. <br><br>Using rubber, that is highly unlikely, impossible with a handheld slingshot. I personally have never even seen a slingshot crossbow that could do that. Maybe a very very long (like 3 meters long) slingshot could do it, but even that is a big challenge.</td></tr>
    </table>
    <span class="postbody"><br>it is possible <a href="http://www.youtube.com/watch?v=eRzTCKMg-lY&feature=plcp" target="_blank" rel="nofollow">http://www.youtube.com/watch?v=eRzTCKMg-lY&feature=plcp</a></span>
    </td></tr>
    </table>
    <span class="postbody"><br><br>I believe that Tordsen TBB will last a few shots and are suitable for light ammo< 5.5 grams and I believe that measurements were done in a really hot day 30°C or more ?? I believe that the only way to achieve 150+ m/s is by means of a mechanic velocity multiplier (cams, or moving arms + pulleys) like in the raptor bow or a crossbow like the flipper at the expense of weight and a fraction of energy transfer ... </span>
     
  18. JoergS

    JoergS Administrator

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    The draw weight you need to propel a 10 gramm projectile to that kind of speed is very high. Plus the bands must be extremely tapered and will tear very early. <br><br>Even the Raptor can only shoot lightweight ammo at high speed, and it has 80 lb draw. In fact very few people can draw that bow. <br><br>My previous postings are based on my sizeable experience in the slingshot field. <br><br>The draw weight I need for the 55 m/s 25mm steel shot is about 24 kg or 53 lb. And I have to shoot butterfly style for that.
     
  19. Awesome thank you for the info Joerg! I have fired bows for years and usually shoot a 60-80 pound draw, and have fired a 100 pound draw for a while, is the draw for slingshots about the same for the same strength draw bow? I have heard mentioned that the farther you draw out a slingshot the harder the draw gets, you think I could handle a shooter with theraband black? My only experience with slingshots so far has been with the marksman brand ones you can buy in stores and the one my great grandfather made me out of a forked branch and some innertube when I was little, neither of which have more than maybe 15 pounds of draw.